Semiconductor structure and method for its production

ABSTRACT

The present invention relates to a semiconductor structure and a method for its production, the semiconductor structure comprising at least one conductor region  9  and at least two semiconductor regions ( 30,40 ), which semiconductor regions are partly separated by the at least one conductor region. The at least one conductor region comprises openings ( 22 ) extending between the semiconductor regions which are partly separated by the respective conductor region. The semiconductor regions comprise at least one organic semiconductor material having a specific HOMO energy level, in particular a DPP polymer. The conductor region comprises a conductive material having a specific work function, said combination of specific energy level and work function allowing for a simple preparation of the conductive region. The invention further relates to a method for providing such a semiconductor structure.

The present invention relates to the field of organic semiconductorstructures, in particular to the field of vertical semiconductorstructures based on diketopyrrolopyrrole (DPP) polymers. In particular,the present invention relates to a semiconductor structure and a methodfor its production, the semiconductor structure comprising at least oneconductor region and at least two semiconductor regions, whichsemiconductor regions are partly separated by the at least one conductorregion, wherein the at least one conductor region comprises openingsextending between the semiconductor regions which are partly separatedby the respective conductor region, wherein the semiconductor regionscomprise at least one organic semiconductor material having a specificHOMO (highest occupied molecular orbital) energy level, in particular aDPP (diketopyrrolopyrrole) polymer, and wherein the conductor regioncomprises a conductive material having a specific work function.

In WO 2010/049321 and in WO 2008/000664, organic semiconductorstructures are described wherein the semiconductor materials arediketopyrrolopyrrole (DPP) polymers. Further, the use of a gateinsulated by a gate dielectric within the structure is generallydisclosed. However, these prior art documents are silent as regards formor structure of the gates.

In US 2006/0086933 A1, an organic semiconductor structure is describedhaving a comb-like electrode or a meshed electrode. The gate electrodeis patterned based on photolithography.

In US 2009/0001362 A1, an organic semiconductor structure is describedhaving a comb-like electrode patterned by electron-beam directlithography.

These patterning methods of the prior art require a substantial amountof time and are not adapted for high throughput processing.

Further, in Yu-Chiang Chao et. al., “High-performance solution-processedpolymer space-charge-limited transistor”, Organic Electronics 9 (2008),pp. 310-316, it is described to use a conductive Al-layer with openingshaving a diameter of 200 nm. Due to their size, openings are formed bydepositing Al and polystyrene spheres which are subsequently removed. Assemiconductors, materials like poly(3-hexylthiophene) are employed. Asto this technique, it is noted that the removal of the polystyrenespheres cannot be reliably realized in an automated high-throughputprocess. In addition, the resulting pattern is based on statisticallyarranged spheres. In particular, a clogging of spheres results inopening sizes depending on the number of spheres per clogged cluster,which can vary to a large extent. Therefore, the pattern cannot bedetermined reliably and inappropriately large opening sizes cannot benot excluded.

US-2009/0181513 A1 as well as Chao et al., Applied Physics Letters 88(2006) 223510, introduce openings to the conductive Al-layer at size of200 nm and 500 nm. Large openings of 200 nm and especially 500 nm showlarge off-current in the transistors, because the small depletion widthbetween Al and poly(hexyl-thiophene) is insufficient to prevent chargetransporting, thus resulting in large off-current and poor transistorperformance.

In Yasuyuki Watanabe et. al., “Characteristics of organic invertersusing vertical- and lateral-type organic transistors”, Thin Solid Films516 (2008), pp. 2731-2734, a transistor structure based on pentacene assemiconductor is shown, in which a gate within the pentacene is in formof slits. However, slits provide a periodic sequence of gate materialand space in between only in one direction, i.e. perpendicular to theslits. Along the slits, gate material and the space in between are notprovided in an alternating manner such that a high gate voltagesensitivity due to the gate material and a high source-drain current dueto the space in between cannot be provided at the same area. Thisresults in poor electrical properties of the transistor.

In US 2005/0196895 A1 as well as in US 2009/0042142 A1, an organicsemiconductor device is shown having a perforated intermediate layer ofconductive material denoted as grid. The openings of the grid areprovided by a patterning die with raised portions of 50-200 nm. The gridis isolated with regard to the organic semiconductor material. As p-typesemiconductor material, organic semiconductor materials like PTCDA, CuPcand a-NPD are proposed. The patterning die mechanically transfers thepattern to the semiconductor material. However, the raised portions inthese sizes, 50-200 nm, cannot be provided in reliable manner due tosignificant tolerances of the pattering die and due to wearing anddeformations of the raised portions. Thus, also electrical properties ofthe semiconductor device resulting from the opening size (gain,drain-source current, etc.) cannot be reproduced in reliable manner.

Therefore, it is an object of the invention to provide a semiconductorstructure and a method for producing such semiconductor structureenabling reliable electrical properties and a high throughput.

Surprisingly, it was found that said object can be solved bysemiconductor structure comprising at least one conductor region and atleast two semiconductor regions, which semiconductor regions are partlyseparated by the at least one conductor region, wherein the at least oneconductor region comprises openings extending between the semiconductorregions which are partly separated by the respective conductor region,wherein the semiconductor regions comprise at least one organicsemiconductor material having a HOMO (highest occupied molecularorbital) energy level E_(H), E_(H) being defined by 5.0 eV≦|E_(H)|≦5.8eV as determined by cyclic voltammetry (see further below), and whereinthe conductor region comprises a conductive material having a workfunction E_(C) being defined by |E_(H)|−1.5 eV≦|E_(C)|≦|E_(H)|−0.4 eV.

Alternative ranges for the energy level E_(H) are: 5.1 eV≦|E_(H)|≦5.8 eVor 5.0 eV≦|E_(H)|≦5.7 eV or, preferably, 5.1 eV≦|E_(H)|≦5.7 eV.

Each of the at least one conductor regions separates two of the at leasttwo semiconductor regions. On each side of each conductor region, one ofthe semiconductor regions contacts the conductor region. The contactsbetween each of the conductor regions and each of the semiconductorregions are Schottky contacts.

The current of free charge carriers between the semiconductor regionsseparated by the at least one conductor region, can be controlled by theconductor region comprising the openings through which the free chargecarriers can pass from one semiconductor region to the semiconductorregion following the conductor region. Thus, the conductor region can beregarded as gate or basis of a vertical transistor formed by thesemiconductor regions and the at least one conductor region. Further,the conductor region can be regarded as grid of a solid equivalent of anelectron tube structure. The at least one conductor region is adapted toimpose an electrical field within at least one of the semiconductorregions by which the current of free charge carriers can be controlled.Such a current of free charge carriers between at least two of thesemiconductor regions is the result of a voltage applied to thesemiconductor regions in the sense of a source-drain voltage, whereinthe current is controlled by the voltage of the conductor region, whichhas the function of a gate. The gate voltage at the conducting regioncontrols the width of the depletion region which extends to the gridopening. The width of the depletion region in turn controls the currentthrough the opening. Particular electrical properties of the inventivesemiconductor structure are the maximum bulk current density of thecurrent through the conductor region as well as the gain defined by thedependency of the current on a control voltage or control currentapplied to the at least one conductive layer. It has been found that theinventive semiconductor structure exhibits significantly improvedelectrical properties.

Further, the improved electrical properties are achieved also in casethat the structural elements of the conductive layer are provided inlarger dimensions. According to the present invention, the semiconductorstructure can be produced with a higher precision since the absoluteinfluence of tolerances or deformations is reduced due to the largergate structures. Further, a plurality of patterning mechanisms can beused, in particular patterning mechanisms adapted for larger structuredimensions only. In addition, a large depletion width can be provided bythe inventive combination of materials. Due to the larger openings, theinfluence of tolerances is decreased, and the precision can be improved.Thus, the electrical properties linked with the structure can be definedwith higher precision. As a consequence, the scrap rate of themanufactured semiconductor structures is significantly decreased.

According to the invention, the at least one conductor region is oneconductor region or more than one conductor regions made of a conductivematerial. As conductive material, materials are denoted which have aspecific electrical resistance of less than 10⁴, less than 10³, lessthan 10², or of less than 10 Ωm. Preferably, the conductive material hasa specific electrical resistance of less than 10⁻³, less than 10⁻⁵, orless than 10⁻⁶ Ωm. Most preferably, the specific electrical resistanceof the conductive material is less than 5×10⁻⁷ Ωm or is less than 1×10⁻⁷Ωm, particularly in the range of the specific electrical resistance ofaluminum.

The conductor region is an integral region and, for each semiconductorregion, all subregions of the semiconductor region are electricallyconnected. Further, a semiconductor region separating two conductorregions coextends with these semiconductor regions or coextends withparts of these semiconductor regions. In particular, the at least oneconductor region and the at least two semiconductor regions can bestacked or be provided in a laminated structure. Within the context ofthe invention, the semiconductor regions are partly separated by the atleast one conductor region, wherein the semiconductor regions areconnected via the openings of the intermediate conductor regions.Further, the conductive material outside the openings, i.e. lateral tothe openings, physically separates the respective semiconductor regions.

The openings within the at least one conductor region are preferably ofthe same shape and are in particular of the same cross-section. Further,the openings have preferably the same cross-sectional area. The openingsare through-holes. This allows to connect semiconductor regions abuttingfrom both sides to the conductor region. The openings extend along adirection inclined to or substantially perpendicular to a direction,along which the conductor region extends.

The semiconductor regions comprise at least one organic semiconductormaterial. The at least one organic semiconductor material is a p-typesemiconductor and provides free positive charges. Further, thesemiconductor material preferably extends through the complete width ofthe respective semiconductor regions. Therefore, the semiconductorregions form an integral semiconducting region. The semiconductorregions enable currents to flow through the complete width of eachsemiconductor region. The semiconductor regions can be provided betweenconductor regions or between an electrode and a conductor region.Further, the semiconductor material of at least of the semiconductorregions extends along the openings such that physical contact is givenbetween semiconductor regions separated by a conductor region by theopenings within the conductor region. This preferably applies to allconductor regions and semiconductor regions of the semiconductorstructure.

The at least one conductor region and the at least two semiconductorregions preferably extend parallel to each other in a stacked fashionproviding a stacked or laminated structure. Additionally, alsoelectrodes can be provided, which also extend parallel to thesemiconductor regions and the at least one conductor region. The atleast one conductor region and the at least two semiconductor regionsare preferably provided as layers. Further, the conductor region extendsfrom one of the semiconductor regions to another one of thesemiconductor regions. Preferably, each of the at least one conductorregion and the at least two semiconductor regions are provided with aconstant thickness, wherein the thickness is given in a directionperpendicular to a direction, in which one of the regions extends.

The organic semiconductor material of the semiconductor regions has aparticular energy level E_(H) corresponding to the energy level of thehighest occupied molecular orbital, which is also denoted as HOMO. TheHOMO level E_(H) reflects the affinity of the organic semiconductormaterial to provide free charge carriers. In particular, the HOMO levelreflects the energy necessary to provide free charge carriers from theorganic semiconductor material and can be compared to an excitationenergy. According to the invention, the absolute value of E_(H) is atleast 5.0 eV or at least 5.1 and does not exceed 5.7 eV or 5.8 eV.Further, the absolute value of the LUMO level, ie. the level of thelowest unoccupied molecular orbital, is preferably 3.3-4.1.

The conductive material of the conductor region according to the presentinvention is adapted to the energy level E_(H) of the semiconductormaterial in order to provide the beneficial electrical and mechanicalproperties of the inventive semiconductor structure. The conductivematerial has a work function E_(C), the absolute value of which is equalto or higher than the absolute value of E_(H) diminished by 1.5 eV. Theabsolute value of the work function E_(C) does not exceed the absolutevalue of E_(H) diminished by 0.4 eV. Therefore, the absolute value ofthe work function E_(C) is less than the absolute value of E_(H). Inparticular, the absolute value of the work function E_(C) differs fromthe absolute value of E_(H) by at least 0.4 eV. Further, the absolutevalue of the work function E_(C) does not differ from the absolute valueof E_(H) by more than 1.5 eV.

In a preferred embodiment, the organic semiconductor material has a bulkconcentration of positive charge carrier equivalents N_(p) withN_(p)≦1×10¹⁶ cm⁻³, N_(p)≦8×10¹⁵ cm⁻³, N_(p)≦6×10¹⁵ cm⁻³, N_(p)≦5×10¹⁵cm⁻³, N_(p)≦10¹⁶ cm⁻³, N_(p)≦4×10¹⁵ cm⁻³, N_(p)≦2×10¹⁵ cm⁻³, orN_(p)≦1×10¹⁵ cm⁻³. Positive charge carrier equivalents are positivecharge distributions within the organic semiconductor material whichhave the electrical effect of free positive charge carriers, for exampleholes. A positive charge carrier equivalent corresponds to a charge unitif the electrostatic effect of the positive charge carrier equivalentcorresponds to the electrostatic effect of a positive free chargecarrier being charged with one charge unit.

Different bulk concentrations within an organic semiconductor materialcan be provided by distinct physical structures of the organicsemiconductor material due to the dependency of the bulk concentrationof charge carrier equivalents within the organic semiconductor materialon its structure. In particular, this applies to organic semiconductormaterial which is deposited as a solution, wherein at least one of theconcentration of the solution, the kind of solvent, the processtemperature, a mechanical pressure exerted on the semiconductormaterial, e.g. a centrifugal force, the process duration and the timeelapsed since the preparation of the solution defines the charge carrierequivalents.

According to a more preferred embodiment, the semiconductor structure isadapted to provide a depletion width I_(d) of at least 100 nm,preferably of at least 125 nm, and most preferably of at least 250 nmwithin the semiconductor region. The depletion width applies to acondition, in which no external voltage is applied to the conductorregion. Further, the semiconductor structure is adapted to provide adepletion width I_(d) of at least 75 nm, at least 100 nm, at least 150nm, at least 200 nm, at least 300 nm, at least 400 nm, at least 500 nm,at least 600 nm, at least 700 nm, at least 800 nm, at least 900 nm, orat least 1 μm. The depletion width can be provided or adapted by atleast one of the energy level E_(H) of the highest occupied molecularorbital of the at least one organic semiconductor material, the workfunction E_(C) of the conductive material and the bulk concentration ofpositive charge carrier equivalents N_(p) at an appropriate level. Thedepletion width is the width of the depletion zone at the condition thatno external voltage is applied to the conductor region.

As far as the materials of the semiconductor regions are concerned, nospecific restrictions exist provided that above-described embodiments ofthe present invention can be realized.

According to a preferred embodiment, at least one of the semiconductorregions of the inventive semiconductor structure contains at least onesuitable diketopyrrolopyrrole (DPP) polymer as semiconductor material.Preferably, at least one of the semiconductor regions comprises, assemiconductor material, at least one suitable DPP polymer. Morepreferably, each of the at least one of the semiconductor regionscomprises, as semiconducting material, at least one suitable DPP polymerwherein the at least one DPP polymer comprised in a given semiconductorregion is the same as or different from the at least one DPP polymer inanother semiconductor region.

Generally, a DPP polymer of the present invention is a polymer havingone or more DPP

skeletons represented by the following formula

in the repeating unit. Examples of DPP polymers and their synthesis are,for example, described in U.S. Pat. No. 6,451,459B1, WO05/049695,WO2008/000664, WO2010/049321, WO2010/049323, WO2010/108873,WO2010/115767, WO2010/136353, PCT/EP2011/060283 and WO2010/136352.

According to a preferred embodiment, the at least one organicsemiconductor material comprises a diketopyrrolopyrrole (DPP) polymerhaving one or more DPP skeletons represented by the following formula

in the repeating unit,

wherein R¹ and R² are the same or different from each other and areselected from the group consisting of hydrogen; a C₁-C₁₀₀ alkyl group;—COOR¹⁰⁶; a C₁-C₁₀₀ alkyl group which is substituted by one or morehalogen atoms, hydroxyl groups, nitro groups, —CN, or C₆-C₁₈ aryl groupsand/or interrupted by —O—, —COO—, —OCO—, or —S—; a C₇-C₁₀₀ arylalkylgroup; a carbamoyl group; a C₅-C₁₂ cycloalkyl group which can besubstituted one to three times with a C₁-C₈ alkyl group and/or a C₁-C₈alkoxy group; a C₆-C₂₄ aryl group, in particular phenyl or 1- or2-naphthyl which can be substituted one to three times with a C₁-C₈alkyl group, a C₁-C₂₅ thioalkoxy group, and/or a C₁-C₂₅ alkoxy group;and pentafluorophenyl;

with R¹⁰⁶ being a C₁-C₅₀ alkyl group, preferably a C₄-C₂₅ alkyl group.

Still more preferably, the DPP polymer comprised in the at least onesemiconductor region of the semiconductor structure of the presentinvention is selected from a group consisting of a polymer of formula(Ia)

*A_(n)*   (Ia)

a copolymer of formula (Ib)

*A-D_(n)*   (Ib)

a copolymer of formula (Ic)

*A-D_(x)B-D_(y)_(n)*   (Ic)

and a copolymer of formula (Id),

*A-D_(r)B-D_(s)A-E_(t)B-E_(u)_(n)*   (Id)

wherein x=0.995 to 0.005, y=0.005 to 0.995, preferably x=0.2 to 0.8,y=0.8 to 0.2, with the proviso that x+y=1;

r=0.985 to 0.005, s=0.005 to 0.985, t=0.005 to 0.985, u=0.005 to 0.985,with the proviso that r+s+t+u=1;

n=4 to 1000, preferably 4 to 200, more preferably 5 to 100,

A is a group of formula

wherein a′=1, 2, or 3, a″=0, 1, 2, or 3; b=0, 1, 2, or 3; b′=0, 1, 2, or3; c=0, 1, 2, or 3; c′=0, 1, 2, or 3; d=0, 1, 2, or 3; d′=0, 1, 2, or 3;with the proviso that b′ is not 0 if a″ is 0;

Ar¹, Ar^(1′), Ar², Ar^(2′), Ar³, Ar^(3′), Ar⁴ and Ar^(4′) areindependently of each other heteroaromatic or aromatic rings, whichoptionally can be condensed and/or substituted, preferably

wherein one of X³ and X⁴ is N and the other is CR⁹⁹;

R⁹⁹, R¹⁰⁴, R^(104′), R¹²³ and R^(123′) are independently of each otherhydrogen, halogen, especially F, or a C₁-C₂₅ alkyl group, especially aC₄-C₂₅ alkyl, which may optionally be interrupted by one or more oxygenor sulphur atoms, C₇-C₂₅ arylalkyl, or a C₁-C₂₅ alkoxy group;

R¹⁰⁵, R^(105′), R¹⁰⁶ and R^(106′) are independently of each otherhydrogen, halogen, C₁-C₂₅ alkyl, which may optionally be interrupted byone or more oxygen or sulphur atoms; C₇-C₂₅ arylalkyl, or C₁-C₁₈ alkoxy;

R¹⁰⁷ is C₂₅ arylalkyl, C₆-C₁₈ aryl; C₆-C₁₈ aryl which is substituted byC₁-C₁₈ alkyl, C₁-C₁₈ perfluoroalkyl, or C₁-C₁₈ alkoxy; C₁-C₁₈ alkyl;C₁-C₁₈ alkyl which is interrupted by —O—, or —S—; or —COOR¹²⁴;

R¹²⁴ is C₁-C₂₅ alkyl group, especially a C₄-C₂₅ alkyl, which mayoptionally be interrupted by one or more oxygen or sulphur atoms, C₇-C₂₅arylalkyl;

R¹⁰⁸ and R¹⁰⁹ are independently of each other H, C₁-C₂₅ alkyl, C₁-C₂₅alkyl which is substituted by E and/or interrupted by D, C₇-C₂₅arylalkyl, C₆-C₂₄ aryl, C₆-C₂₄ aryl which is substituted by G, C₂-C₂₀heteroaryl, C₂-C₂₀ heteroaryl which is substituted by G, C₂-C₁₈ alkenyl,C₂-C₁₈ alkynyl, C₁-C₁₈ alkoxy, C₁-C₁₈ alkoxy which is substituted by Eand/or interrupted by D, or C₇-C₂₅ aralkyl; or

R¹⁰⁸ and R¹⁰⁹ together form a group of formula ≡CR¹¹⁰R¹¹¹, wherein

R¹¹⁰ and R¹¹¹ are independently of each other H, C₁-C₁₈ alkyl, C₁-C₁₈alkyl which is substituted by E and/or interrupted by D, C₆-C₂₄ aryl,C₆-C₂₄ aryl which is substituted by G, or C₂-C₂₀ heteroaryl, or C₂-C₂₀heteroaryl which is substituted by G; or

R¹⁰⁸ and R¹⁰⁹ together form a five or six-membered ring, whichoptionally can be substituted by C₁-C₁₈ alkyl, C₁-C₁₈alkyl which issubstituted by E and/or interrupted by D, C₆-C₂₄ aryl, C₆-C₂₄ aryl whichis substituted by G, C₂-C₂₀ heteroaryl, C₂-C₂₀ heteroaryl which issubstituted by G, C₂-C₁₈ alkenyl, C₂-C₁₈ alkynyl, C₁-C₁₈ alkoxy, C₁-C₁₈alkoxy which is substituted by E and/or interrupted by D, or C₇-C₂₆aralkyl;

D is —CO—, —COO—, —S—, —O—, or NR¹¹²—;

E is C₁-C₈ thioalkoxy, C₁-C₈ alkoxy, CN, —NR¹¹²R¹¹³, —CONR¹¹²R¹¹³, orhalogen,

G is E, or C₁-C₁₈ alkyl, and

R¹¹² and R¹¹³ are independently of each other H; C₆-C₁₈ aryl; C₆-C₁₈aryl which is substituted by C₁-C₁₈ alkyl, or C₁-C₁₈ alkoxy; C₁-C₁₈alkyl; or C₁-C₁₈ alkyl which is interrupted by —O— and

B, D and E are independently of each other a group of formula

*Ar⁴_(k) ^(Ar) ⁵_(l)Ar⁶_(r)Ar⁷_(z)*

or formula (X), with the proviso that in case B, D and E are a group offormula (X), they are different from A, wherein k=1; l=0 or 1; r=0 or 1;z=0 or 1; and

Ar⁴, Ar⁵, Ar⁶ and Ar⁷ are independently of each other a group of formula

wherein one of X⁵ and X⁶ is N and the other is CR¹⁴,

c is an integer of 1, 2, or 3,

d is an integer of 1, 2, or 3,

Ar⁸ and Ar^(8′) are independently of each other a group of formula

X¹ and X² are as defined above,

R^(1″) and R^(2″) may be the same or different and are selected fromhydrogen, a C₁-C₃₆ alkyl group, especially a C₆-C₂₄ alkyl group, aC₆-C₂₄ aryl, in particular phenyl or 1- or 2-naphthyl which can besubstituted one to three times with C₁-C₈ alkyl, C₁-C₈ thioalkoxy,and/or C₁-C₈ alkoxy, or pentafluorophenyl,

R¹⁴, R^(14′), R¹⁷ and R^(17′) are independently of each other H, or aC₁-C₂₅ alkyl group, especially a C₆-C₂₆ alkyl, which may optionally beinterrupted by one or more oxygen atoms.

Ar¹ and Ar^(1′) are preferably

more preferably

is most preferred.

Ar², Ar^(2′), Ar³, Ar^(3′), Ar⁴ and Ar^(4′) are preferably

more preferably

The group of formula *Ar⁴_(k)Ar⁵_(l)Ar⁶_(r)Ar⁷_(z)* ispreferably

more preferably

most preferred

R¹ and R² may be the same or different and are preferably selected fromhydrogen, a C₁-C₁₀₀alkyl group, especially a C₈-C₃₆alkyl group.

The group A is preferably selected from

The group of formula *Ar⁴_(k)Ar⁵_(l)Ar⁶_(r)Ar⁷_(z)* ispreferably a group of formula

Examples of preferred DPP polymers of formula Ia are, for example:

Examples of preferred DPP polymers of formula Ib are, for example:

Examples of preferred DPP polymers of formula Ic are, for example:

In particular in above-described preferred DPP polymers of structures(Ia), (Ib), and (Ic), the groups R¹ and R² are, independently from eachother, a C₁-C₃₆alkyl group, especially a C₈-C₃₆alkyl group. n ispreferably 4 to 1000, especially 4 to 200, very especially 5 to 100. R³is preferably a C₁-C₁₈alkyl group. R¹⁵ is preferably a C₄-C₁₈alkylgroup. As far as the indices are concerned, x is preferably in the rangefrom 0.995 to 0.005, and y is preferably in the range from 0.005 to0.995. More preferably, x=0.4 to 0.9, and y=0.6 to 0.1, with x+y=1.

According to an especially preferred embodiment of the presentinvention, the at least one DPP polymer comprised in the at least onesemiconductor region is a DPP polymer of structure (Ib), even morepreferably of structure (Ib-1), (Ib-9), (Ib-10). Therefore, the presentinvention relates to above-described semiconductor structure, whereinthe DPP polymer is, for example, a polymer according to formula (Ib-1)

wherein R¹ and R² are independently from each other a C₈-C₃₆ alkylgroup,

with n=4 to 1000, preferably 4 to 200, more preferably 5 to 100. Oneespecially preferred DPP polymer according to structure (Ib-1) is, forexample,

with Mw=39,500, and a polydispersity=2.2 (measured by HT-GPC)).Reference is made, for example, to Example 1 of WO2010/049321.

Halogen is fluoro, chloro, bromo, iodo, especially fluoro.

C₁-C₂₅alkyl (C₁-C₁₈alkyl) is typically linear or branched, wherepossible. Examples are methyl, ethyl, n-propyl, isopropyl, n-butyl,sec.-butyl, isobutyl, tert.-butyl, n-pentyl, 2-pentyl, 3-pentyl,2,2-dimethylpropyl, 1,1,3,3-tetramethylpentyl, n-hexyl, 1-methylhexyl,1,1,3,3,5,5-hexamethylhexyl, n-heptyl, isoheptyl,1,1,3,3-tetramethylbutyl, 1-methylheptyl, 3-methylheptyl, n-octyl,1,1,3,3-tetramethylbutyl and 2-ethylhexyl, n-nonyl, decyl, undecyl,dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl,octadecyl, eicosyl, heneicosyl, docosyl, tetracosyl or pentacosyl.C₁-C₈alkyl is typically methyl, ethyl, n-propyl, isopropyl, n-butyl,sec.-butyl, isobutyl, tert.-butyl, n-pentyl, 2-pentyl, 3-pentyl,2,2-dimethyl-propyl, n-hexyl, n-heptyl, n-octyl,1,1,3,3-tetramethylbutyl and 2-ethylhexyl. C₁-C₄alkyl is typicallymethyl, ethyl, n-propyl, isopropyl, n-butyl, sec.-butyl, isobutyl,tert.-butyl.

C₁-C₂₅alkoxy (C₁-C₁₈alkoxy) groups are straight-chain or branched alkoxygroups, e.g. methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy,sec-butoxy, tert-butoxy, amyloxy, isoamyloxy or tert-amyloxy, heptyloxy,octyloxy, isooctyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy,tetradecyloxy, pentadecyloxy, hexadecyloxy, heptadecyloxy andoctadecyloxy. Examples of C₁-C₈alkoxy are methoxy, ethoxy, n-propoxy,isopropoxy, n-butoxy, sec.-butoxy, isobutoxy, tert.-butoxy, n-pentoxy,2-pentoxy, 3-pentoxy, 2,2-dimethylpropoxy, n-hexoxy, n-heptoxy,n-octoxy, 1,1,3,3-tetramethylbutoxy and 2-ethylhexoxy, preferablyC₁-C₄alkoxy such as typically methoxy, ethoxy, n-propoxy, isopropoxy,n-butoxy, sec.-butoxy, isobutoxy, tert.-butoxy. The term “alkylthiogroup” means the same groups as the alkoxy groups, except that theoxygen atom of the ether linkage is replaced by a sulfur atom.

C₂-C₂₅alkenyl (C₂-C₁₈alkenyl) groups are straight-chain or branchedalkenyl groups, such as e.g. vinyl, allyl, methallyl, isopropenyl,2-butenyl, 3-butenyl, isobutenyl, n-penta-2,4-dienyl,3-methyl-but-2-enyl, n-oct-2-enyl, n-dodec-2-enyl, isododecenyl,n-dodec-2-enyl or n-octadec-4-enyl.

C₂₋₂₄alkynyl (C₂₋₁₈alkynyl) is straight-chain or branched and preferablyC₂₋₈alkynyl, which may be unsubstituted or substituted, such as, forexample, ethynyl, 1-propyn-3-yl, 1-butyn-4-yl, 1-pentyn-5-yl,2-methyl-3-butyn-2-yl, 1,4-pentadiyn-3-yl, 1,3-pentadiyn-5-yl,1-hexyn-6-yl, cis-3-methyl-2-penten-4-yn-1-yl,trans-3-methyl-2-penten-4-yn-1-yl, 1,3-hexadiyn-5-yl, 1-octyn-8-yl,1-nonyn-9-yl, 1-decyn-10-yl, or 1-tetracosyn-24-yl.

C₅-C₁₂cycloalkyl is typically cyclopentyl, cyclohexyl, cycloheptyl,cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl, cyclododecyl,preferably cyclopentyl, cyclohexyl, cycloheptyl, or cyclooctyl, whichmay be unsubstituted or substituted. The cycloalkyl group, in particulara cyclohexyl group, can be condensed one or two times by phenyl whichcan be substituted one to three times with C₁-C₄-alkyl, halogen andcyano. Examples of such condensed

cyclohexyl groups are:

in particular

wherein R¹⁵¹, R¹⁵², R¹⁵³, R¹⁵⁴, R¹⁵⁵ and R¹⁵⁶ are independently of eachother C₁-C₈-alkyl, C₁-C₈-alkoxy, halogen and cyano, in particularhydrogen.

C₈-C₂₄aryl (C₈-C₁₈aryl) is typically phenyl, indenyl, azulenyl,naphthyl, biphenyl, as-indacenyl, s-indacenyl, acenaphthylenyl,fluorenyl, phenanthryl, fluoranthenyl, triphenlenyl, chrysenyl,naphthacen, picenyl, perylenyl, pentaphenyl, hexacenyl, pyrenyl, oranthracenyl, preferably phenyl, 1-naphthyl, 2-naphthyl, 4-biphenyl,9-phenanthryl, 2- or 9-fluorenyl, 3- or 4-biphenyl, which may beunsubstituted or substituted. Examples of C₈-C₁₂aryl are phenyl,1-naphthyl, 2-naphthyl, 3- or 4-biphenyl, 2- or 9-fluorenyl or9-phenanthryl, which may be unsubstituted or substituted.

C₇-C₂₅aralkyl is typically benzyl, 2-benzyl-2-propyl, β-phenyl-ethyl,α,α-dimethylbenzyl, ω-phenyl-butyl, ω,ω-dimethyl-ω-phenyl-butyl,ω-phenyl-dodecyl, ω-phenyl-octadecyl, ω-phenyl-eicosyl orω-phenyl-docosyl, preferably C₇-C₁₈aralkyl such as benzyl,2-benzyl-2-propyl, β-phenyl-ethyl, α,α-dimethylbenzyl, ω-phenyl-butyl,ω,ω-dimethyl-ω-phenyl-butyl, ω-phenyl-dodecyl or ω-phenyl-octadecyl, andparticularly preferred C₇-C₁₂aralkyl such as benzyl, 2-benzyl-2-propyl,β-phenyl-ethyl, α,α-dimethylbenzyl, ω-phenyl-butyl, orω,ω-dimethyl-ω-phenyl-butyl, in which both the aliphatic hydrocarbongroup and aromatic hydrocarbon group may be unsubstituted orsubstituted. Preferred examples are benzyl, 2-phenylethyl,3-phenylpropyl, naphthylethyl, naphthylmethyl, and cumyl.

The term “carbamoyl group” typically stands for a C₁₋₁₈carbamoylradical, preferably C₁₋₈carbamoyl radical, which may be unsubstituted orsubstituted, such as, for example, carbamoyl, methylcarbamoyl,ethylcarbamoyl, n-butylcarbamoyl, tert-butylcarbamoyl,dimethylcarbamoyloxy, morpholinocarbamoyl or pyrrolidinocarbamoyl.

Heteroaryl is typically C₂₋C₂₈heteroaryl (C₂₋C₂₀heteroaryl), i.e. a ringwith five to seven ring atoms or a condensed ring system, whereinnitrogen, oxygen or sulfur are the possible hetero atoms, and istypically an unsaturated heterocyclic group with five to 30 atoms havingat least six conjugated π-electrons such as thienyl, benzo[b]thienyl,dibenzo[b,d]thienyl, thianthrenyl, furyl, furfuryl, 2H-pyranyl,benzofuranyl, isobenzofuranyl, dibenzofuranyl, phenoxythienyl, pyrrolyl,imidazolyl, pyrazolyl, pyridyl, bipyridyl, triazinyl, pyrimidinyl,pyrazinyl, pyridazinyl, indolizinyl, isoindolyl, indolyl, indazolyl,purinyl, quinolizinyl, chinolyl, isochinolyl, phthalazinyl,naphthyridinyl, chinoxalinyl, chinazolinyl, cinnolinyl, pteridinyl,carbazolyl, carbolinyl, benzotriazolyl, benzoxazolyl, phenanthridinyl,acridinyl, pyrimidinyl, phenanthrolinyl, phenazinyl, isothiazolyl,phenothiazinyl, isoxazolyl, furazanyl or phenoxazinyl, which can beunsubstituted or substituted.

Possible substituents of the above-mentioned groups are C₁-C₈alkyl, ahydroxyl group, a mercapto group, C₁-C₈alkoxy, C₁-C₈alkylthio, halogen,halo-C₁-C₈alkyl, a cyano group, a carbamoyl group, a nitro group or asilyl group, especially C₁-C₈alkyl, C₁-C₈alkoxy, C₁-C₈alkylthio,halogen, halo-C₁-C₈alkyl, or a cyano group.

If, according to a conceivable embodiment, the inventive semiconductorstructure has two semiconductor regions which are partly separated bythe one conductor regions, it is preferred that each of the twosemiconductor regions comprises at least one DPP polymer of structure(Ib), more preferably at least one DPP polymer of structure (Ib-1), evenmore preferably at least one DPP polymer of structure (Ib-1) wherein R¹and R² are independently from each other a C₈-C₃₆ alkyl group, with n=4to 1000, preferably 4 to 200, more preferably 5 to 100. According to aneven more preferred embodiment of the present invention, bothsemiconductor regions contain the same DPP polymers, even morepreferably exactly one DPP polymer.

In particular, the polydispersity of the polymer comprised by the atleast one organic semiconductor material, preferably the at least oneDPP polymer, has a polydispersity in the range of from 1.01 to 10,preferably from 1.1 to 3.0 and more preferably from 1.5 to 2.5.

The openings within the at least one conductor region have an innerwidth of at least 200 nm, preferably at least 250 nm and most preferablyat least 500 nm. Further, the inner width of the openings can be atleast 150 nm, at least 200 nm, at least 300 nm, at least 400 nm, atleast 600 nm, at least 800 nm, at least 1000 nm, at least 1200 nm, atleast 1400 nm, at least 1600 nm, at least 1800 nm, or at least 2 μm. Avariety of simple approaches can be used for providing such openings. Inparticular due to the large inner size of the openings, the openings canbe easily provided with mechanical methods. Particular method steps forproviding such openings are given below in the context of the inventivemethod. The openings have a substantially circular inner cross section.

According to an embodiment of the present invention, the openings withinthe at least one conductor region are embossed openings, mechanicallycut openings or laser-cut openings. In particular, the openings can beembossed openings, which are formed by pressing into a layer ofconductive material. A patterned matrix can be used, which is pressedinto the conductive layer such that the resulting openings are formed bymechanical removal of the conductive material. Thus, the openings can beformed by the formation using a patterned matrix. Further, the openingscan be formed by cutting, wherein two cutting matrices are used whichare pressed into a layer of the conductive material from both sides ofthe layer thereby cutting conductive material from the location of theopenings. In particular, such matrices used for providing the openingscan have the shape of rollers. In case that embossed openings areprovided, the layer of conducting material can be an individual layer ora layer supported by a substrate, e.g. supported by a semiconductorregion. Further, the openings can be laser-cut openings formed byevaporation of conducting material within a layer at the locations ofthe openings. In the case of laser-cut openings, the openings can beformed within an individual layer of conductive material forming theconductor region or can be formed by a layer supported by substrate,e.g. by a semiconductor region. The conductor region comprising theopenings can be provided by a foil, a sheet or a deposited layer ofconductive material.

The conductive material of the conductor region comprises or preferablyconsists of a metal, of an alloy or of a conductive polymer, preferablya metal, more preferably a metal selected from the group consisting ofAl, Cr, Cu, Fe, In, Sb, Si, Sn, and Zn, wherein the metal is inparticular Al. The alloy is preferably an alloy comprising at least twoof these metals. The conductive material can be provided as a homogenousstructure of the metal, the alloy or the conductive polymer, or can be acompound comprising at least two of the metal, the alloy or theconductive polymer. In a particular embodiment, the conductive materialis provided by nanotubes, which can be provided within a matrix of themetal, the alloy or the conductive polymer. In another embodiment, theconductive material is provided by a semiconducting material, which ishighly doped. Since highly doped semiconductor materials provide highelectrical conductivity, such highly doped semiconductor materials areregarded as conductive materials in the sense of the invention as far asthey exhibit a specific electrical resistance of the conductor material.In addition, instead of the metal or the alloy, an electricallyconducting compound thereof can be used. In particular, indium tin oxidecan be used as conductive material. In particular, the highly dopedsemiconductor material is a semiconductor material doped with a p-dopantor, preferably, an n-dopant at a high concentration leading to highelectrical conductivity. The conductive material and in particular thehighly doped semiconductor material has a specific electricalresistivity of less than 1×10², less than 1×10¹, or less than 1 Ωm.

The present invention thus includes a semiconductor structure comprisingat least one conductor region and at least two semiconductor regions,which semiconductor regions are partly separated by the at least oneconductor region, wherein the at least one conductor region comprisesopenings extending between the semiconductor regions which are partlyseparated by the respective conductor region, wherein the semiconductorregions comprise at least one organic semiconductor material selectedfrom DPP polymers described above, and wherein the conductor regioncomprises a metal selected from the group consisting of Al, Cr, Cu, Fe,In, Sb, Si, Sn, and Zn, the metal in particular being Al.

An embodiment of the inventive semiconductor structure comprises atleast two electrodes at end faces of the semiconductor regions,preferably one electrode at each of both end faces of the semiconductorregions. The electrodes as well as the conductor region each comprise acontact region or are provided with a conductor adapted for externalcontact. The electrodes are provided at faces of the semiconductorregion, which are not covered by a conductor region. Preferably, allconductor regions are located between two semiconductor regions and,consequently, are located between two electrodes. The electrodescoextend with the semiconductor regions and the at least one conductorregion. Electrodes are provided by conductive material, preferably by aconductive material having a work function E_(E) with|E_(E)|≧|E_(H)|−0.3 eV. Further, the absolute value of the work functionE_(E) of the electrode material is preferably less than or equal to|E_(H)|+0.9 eV. The electrodes are an integral layer, which ispreferably continuous. As an example, the electrodes substantiallyconsist of Au or Ag. However, also other conducting materials can beused, e.g. indium tin oxide or zinc oxide or a material comprises atleast one conducting polymer. If the conductor is provided for externalcontact, the conductor at least partly extends laterally to theelectrode. In addition, each of the electrodes can have a multilayeredsubstructure, wherein the electrode material having a work function ofE_(E) is provided by a coating of the substructure abutting to thesemiconductor region or semiconductor regions, and wherein this coatingis provided on an electrically conductive substrate with the workfunction of E_(E). The semiconductor regions which are partly separatedby the respective conductor region are in direct contact with each otherthrough the openings of said conductor region. The semiconductor regionsare separated by the respective conductor region by sections of therespective conductor region lateral to the openings. The semiconductorregions are separated by the material of the conductor region within thesections lateral to the openings. These sections are provided forapplying an electrical field to at least one of the semiconductorregions. The semiconductor regions on both sides of the respectiveconductor region are physically connected to each other via theopenings. Preferably, semiconductor material extending through openingsforms a continuous inner opening section. The semiconductor regions areon both sides of the respective conductor region and are continuouslyand physically connected with each other, preferably via the inneropening section of the semiconductor material. In this way, theinventive semiconductor structure is adapted to provide transfer of freecharge carriers between semiconductor regions partly separated by theconductor region.

The inventive semiconductor structure comprises or, preferably,substantially consists of a conductor region partly separating twosemiconductor regions. The conductor region and the two semiconductorregions provide a vertical transistor structure, wherein the conductorregion provides a gate, a basis or a grid adapted for conductivitycontrol between the semiconductor regions. A particular embodiment ofsuch a semiconductor structure comprises one conductor region separatingtwo semiconductor regions, as well as two electrodes. The end faces ofeach of the semiconductor regions opposite to the conductor region eachcarry one of the electrodes. The resulting vertical transistor structureis adapted to controllably provide current between the electrodes,wherein the current is controlled by a voltage or a current between thegate, i.e. the conductor region on one side and one of the electrodes onthe other side. In such a structure, preferably each of the twosemiconductor regions comprises the same organic semiconductor material,preferably the same DPP polymer. In particular, each of the twosemiconductor regions consists of the same organic semiconductormaterial, preferably the same DPP polymer.

The organic semiconductor material of at least one of the semiconductorregions is most preferably a cast material, in particular a spin-castmaterial, coated material or printed material. A cast material isprovided by a solution of the organic semiconductor material within atleast one solvent, and by removing such a solvent, e.g. by evaporation.The electrical properties of the semiconductor material can be set by amicrostructure of the organic semiconductor material, wherein themicrostructure is mainly defined by the deposition method of the castmaterial. Further, the material can be printed in form of dissolvedsemiconductor material. In particular, the semiconductor material can beinkjet-printed material. Inkjet-printed material can be provided in adesired pattern in order to pattern the semiconductor structure in adirection along which the semiconductor structure extends.

According to a further aspect of the invention, a method for producingan inventive semiconductor structure is provided. The method comprisesthe following steps:

-   -   (a) providing at least two semiconductor regions comprising at        least one organic semiconductor material;    -   (b) providing at least one conductor region between the at least        two semiconductor regions;    -   (c) providing openings in the at least one conductor region        extending through the entire conductor region; and    -   (d) partly contacting the at least two semiconductor regions        through the openings of the at least one conductor region.

In a preferred method, step (b) comprises providing the at least oneconductor region as a continuous layer of the conductive material andstep (c) comprises embossing, mechanically cutting or laser cutting theopenings with an inner width of the openings of more than 200 nm,preferably more than 250 nm, more preferably more than 500 nm, throughthe continuous layer. In this preferred method step (b), at least one ofthe conductor regions usually is provided as an individual continuoussheet, and step (c) is carried out before (b) is completed and before,during or after the conductor region is joined with one of the at leasttwo semiconductor regions. The individual continuous sheet preferably isa prefabricated sheet.

Alternatively, said preferred method may be carried out in that in step(b), at least one of the conductor regions is deposited onto one of theat least two semiconductor regions provided in (a), preferably by vapordeposition, and step (c) is carried out before (b) is completed andduring or after the conductor region is deposited.

Also preferred is a method, wherein, for each of the semiconductorregions, (a) comprises applying the organic semiconductor material ontoa substrate or onto the at least one conductor region in one or moresteps, wherein the organic semiconductor material is applied infree-flowing form as a solution, suspension, or emulsion comprising theorganic semiconductor material, preferably by casting, spraying orprinting, or wherein the organic semiconductor material is applied insolid form, and wherein (d) comprises applying the organic semiconductormaterial of at least one of these semiconductor regions into theopenings, in particular by casting, and preferably in the course of (a).According to this method, the organic semiconductor material often isprovided as a solution or dispersion of the material in at least oneorganic solvent, the solution preferably having a content of 0.5 to 20weight-% of the organic semiconductor material, relative to the totalweight of the solution or dispersion. The solution or dispersion may bespin cast on the substrate.

In a preferred method, the above process is carried out performing thefollowing steps:

-   -   (i) providing at least one semiconductor region comprising at        least one organic semiconductor material;    -   (ii) providing at least one conductor region in contact to the        semiconductor region;    -   (iii) providing openings in the at least one conductor region        extending through the entire conductor region;    -   (iv) providing at least one semiconductor region comprising at        least one organic semiconductor material in contact with the        conductor region in way that conductor region is between at        least two semiconductor regions; and    -   (v) partly contacting the at least two semiconductor regions 5        through the openings of the at least one conductor region.

One embodiment of steps (ii) and (iii) of said method is applying aconductor having pre-formed openings (ii), another embodiment thereofcomprises the forming the openings after applying to the 1stsemiconductor (iii), i.e.

(a) providing at least one conductor region with openings in the atleast one conductor region extending through the entire conductor regionin contact to the semiconductor region ; or

(b) providing at least one conductor region in contact to thesemiconductor region, and subsequently providing openings in the atleast one conductor region extending through the entire conductorregion.

When the 2nd semiconductor region is provided (step iv), contact withthe 1st semiconductor layer through openings (step v) may be formed as aseparate step or preferably immediately.

Furthermore preferred is a method, wherein at least two electrodes areapplied to end faces of the semiconductor regions by depositing anelectrode material onto at least one of the end faces, or by providingthe electrode material, onto which at least one of the semiconductorregions is applied, wherein the electrode material is preferably Au, Ag,Pt, Pd or an alloy of at least two of these materials.

The organic semiconductor material of step (a) has a HOMO (highestoccupied molecular orbital) energy level E_(H), E_(H) being defined by5.0 eV≦|E_(H)|≦5.8 eV. The at least one conductor region provided instep (b) comprises a conductive material having a work function E_(C)being defined by |E_(H)|=1.5 eV≦|E_(C)|≦|E_(H)|−0.4 eV.

Alternatives for the range of the energy level E_(H) are: 5.1eV≦|E_(H)|≦5.8 eV, 5.0 eV≦|E_(H)|≦5.7 eV or preferably 5.1eV≦|E_(H)|≦5.7 eV.

HOMO/LUMO values are obtained experimentally using cyclic voltammetry(Autolab PGSTAT30® Potentiostat), using Pt working electrode, Ag counterelectrode and AgCl coated Ag as pseudo-reference electrode; electrolyteis 0.1M tetrabutylammonium hexafluorophosphate in o-dichlorobenzene;internal reference is ferrocene.

In particular, the semiconductor regions, the organic semiconductormaterial, the at least one conductor region and/or the conductivematerial are provided according to the definitions provided above withregard to the inventive semiconductor structure.

Preferably, step (b) comprises providing at least one conductor regionas a continuous layer of the conductive material. Further, step (c)comprises embossing, mechanically cutting or laser-cutting the openingswith an inner width of the openings of more than 200 nm, preferably morethan 250 nm, more preferably more than 500 nm, through the continuouslayer. In particular, the openings provided by step (c) are providedwith an inner width of at least 150 nm, 200 nm, 300 nm, 400 nm or 600nm. In addition, the inner width can be at least 800 nm, at least 1000nm, at least 1200 nm, at least 1400 nm, at least 1600 nm, at least 1800nm or at least 2 μm. The conductor region can be coated and the openingscan be provided after having applied the continuous layer as a coating.Alternatively, the conductor region can be applied by patterning suchthat the openings are formed when the conductor region is provided.

The conductor region can be provided by coating or patterning theconductive material, in particular by coating or patterning theconductive material dissolved in a solvent. The conductive material canbe spray-coated, printed, in particular inkjet-printed, deposited, e.g.by chemical vapor deposition, or by other suitable coating or patterningmethods. Generally, subtractive or additive methods for providing theconductor region can be used. In particular, these methods arerole-to-role techniques. The additive methods include deposition, inparticular by evaporation, sputtering, coating or printing of theconductive material. The pattern is formed by removal or modification ofthe conductive material. In particular, removal includes lithographicalmethods combined with etching, lift-off, delamination or laserablation/laser cutting of the conductive material. Modification includesembossing, oxidation, light exposure or chemical treatment of theconductive material. The subtractive methods include printing, e.g.gravure, screen printing, flexo printing or p-contact printing. Further,the subtractive methods include the application of the shadow maskbefore adding the conductive material, wherein the conductive materialis added by evaporation or sputtering. In addition, the subtractivemethods include transfer of conductive material, in particular bystamping, by lamination or by thermal transfer.

These methods can also be used to provide electrodes at end faces of thesemiconducting material, wherein electrode material takes the place ofthe conductive material.

Advantageously, at least one of the conductor regions is provided as anindividual continuous sheet. Further, step (c) of providing the openingsis carried out before step (b) of providing the at least one conductiveregion is completed. The openings can be provided in the at least oneconductor region by using an individual continuous sheet, perforatingthis individual continuous sheet by embossing, mechanically cutting orlaser-cutting and by applying the perforated continuous sheet onto thesemiconductor region, in particular by lamination. Further, the openingscan be provided by joining the continuous sheet with one of thesemiconductor regions as one step, e.g. by rolling the continuous sheetonto the semiconductor region using a roller comprising an outerstructure adapted for pressing or cutting the openings into the sheet.Therefore, the roller presses the sheet onto the semiconductor region inorder to join the conductor region and the semiconductor region and, atthe same time, embosses or cuts the openings into the sheet. Further,the openings can be provided after the conductor region is joined withthe semiconductor region by laser-cutting, by mechanically cutting or byembossing. In this way, the conductor region is joined with thesemiconductor region as a first step, e.g. by lamination or by vapordeposition, and, as a subsequent second step, openings are cut orembossed into the sheet, which is already joined with the semiconductorregion. Preferably, embossing is provided by nano imprinting usingstamps having a structure complementary to the structure of theopenings.

In an exemplifying embodiment, the individual continuous sheet is aprefabricated sheet. The individual continuous sheet is already providedwith all structural features before joining the sheet with thesemiconductor region. The prefabricated sheet and the conductor regionwithin the semiconductor structure provide the same structural featuresincluding the openings.

In another embodiment, the at least one conductor region is depositedonto one of the at least two semiconductor regions provided in step (a).The at least one conductor region is preferably deposited by vapordeposition. Step (c) of providing the openings is carried out beforestep (b) of providing the at least one conductor region is completed andduring or after the the conductor region is deposited. Therefore, theopenings are provided according to step (c) during or after theconductor region is joined with one of the at least two semiconductorregions. Therefore, the openings are embossed, mechanically cut orlaser-cut into the conductor region, which is already joined with theadjacent semiconductor region.

For each of the semiconductor regions, step (a) comprises applying theorganic semiconductor material onto a substrate or onto the at least oneconductor region in one or more steps. The organic semiconductormaterial is applied in free-flowing form as a solution, suspension oremulsion comprising the organic semiconductor material, preferably bycasting, spraying or printing. Alternatively, the organic semiconductormaterial is applied in solid form, wherein step (d) comprises applyingthe organic semiconductor material of at least one of thesesemiconductor regions into the openings, in particular by casting, andpreferably in the course of step (a) of providing the semiconductorregions. The organic semiconductor material is applied in free-flowingform, in particular by spray-coating, knife-coating or other appropriatedeposition techniques.

Suitable coating methods for applying the semiconductor material includespin-coating, slot-die coating (also called extrusion coating), curtaincoating, reverse gravure coating, blade coating, spray coating and dipcoating.

Suitable printing methods for applying the semiconductor materialinclude inkjet printing, flexography printing, gravure printing, inparticular forward gravure printing, screen printing, pad printing,offset printing and reverse offset printing.

Spin coating and inkjet printing are the preferred methods. Generally,the same or distinct methods for applying the at least two semiconductorregions. In particular, one of the at least two semiconductor regionscan be provided by spin coating and another one of these at least twosemiconductor regions can be provided by inkjet printing.

Further, the organic semiconductor material can be applied in solidform, in particular as a solid layer of semiconductor material, which isapplied by laminating.

The organic semiconductor material of at least one of thesesemiconductor regions is applied into the openings, in particular bycasting the semiconductor material in liquid form, in particular as asolution. In this way, the openings are filled with semiconductormaterial in order to provide a physical contact between twosemiconductor regions separated by a conductor region comprising theopenings. The application of the semiconductor material into theopenings can be supported by pressing semiconductor material towards theopenings, e.g. by spin-coating or by pressing a surface onto thesemiconductor material towards the openings.

When applying the organic semiconductor material in free-flowing form,the semiconductor material is provided as a solution or dispersion ofthe material in at least one organic solvent. The solution preferablyhas a content of 0.1 to 20 wt.-% of the organic semiconductor material.Particularly, the content is 0.1 to 8 wt.-%, for example 1 to 8 wt.-%,more particularly 0.5 to 4 wt.-% or 1 to 2 wt.-% of the organicsemiconductor material; further advantageous ranges of the semiconductormaterial are 2 to 6 wt.-%, or 3 to 5 wt.-%. Advantageously, the contentof organic semiconductor material does not exceed 10 wt.-% or 8 wt.-%,or even 5 wt.-%, and is at least 0.5 wt.-%, preferably at least 1 wt.-%,more preferably at least 2 wt.-%. The organic solvent may be a singlesolvent or a binary solvent (i.e. mixture of two or more solvents); itcan be used with or without additives. In particular, a dichlorobenzenecan be used, preferably 1,2-dichlorobenzene or 1,3-dichlorobenzene.Further, toluene can be used as solvent.

Suitable solvents preparing the formulations according to the presentapplication are organic solvents, in which the DPP polymer and possibleadditives have satisfactory solubility. Examples of further suitableorganic solvents include, but are not limited to,

petroleum ethers, aromatic hydrocarbons such as benzene, chlorobenzene,dichlorobenzene, trichlorobenzene, cyclohexylbenzene, toluene, anisole,xylene, naphthalene, chloronaphtalene, tetraline, indene, indane,cyclooctadiene, styrene, decaline and mesitylene; halogenated aliphatichydrocarbons such as dichloromethane, chloroform and ethylenechloride;ethers such as dioxane and dioxolane; ketones such as cyclopentanone andcyclohexanone; aliphatic hydrocarbons such as hexanes and cyclohexanes;and mixtures of two or more of said solvents.

Preferred solvents are dichlorobenzene, toluene, xylene, tetraline,chloroform, mesitylene and mixtures of two or more thereof.

Preferably, the organic semiconductor material is applied infree-flowing form, as a solution, in particular as a solution of thesemiconductor material in at least one organic solvent, wherein thesolution is spin-cast on the substrate, onto which the organicsemiconductor material is applied. The substrate and/or the solution canbe heated at a temperature of at least 45° C., at least 60° C., andpreferably at least 70° C. during the application of the semiconductormaterial. Further, the temperature of the substrate or the organicsemiconductor material during its application does not exceed 150° C.,140° C. or preferably 120° C. In particular, during the application ofthe semiconductor material, the temperature of the solution and/or thesubstrate does not exceed the boiling point of the at least one organicsolvent. However, the semiconductor material (as well as the substrate,if applicable) is preferably at room temperature during its application.

In order to remove the at least one solvent, the substrate and/or thesolution are heated in order to force the evaporation of the at leastone solvent. The solvent is removed after the application of thesemiconductor material in dissolved form. The heating can be carried outby applying a hot air stream, by directing infrared radiation onto thesubstrate and/or the solution or by placing the substrate and/or thesolution onto a hot plate or into a drying oven.

For preferred embodiments, the semiconductor material is applied at roomtemperature (20° C.). The semiconductor material is dried at a highertemperature, however preferably below the boiling of the solvent. Thesemiconductor material is preferably dried at a temperature of at least45° C., at least 60° C., and advantageously at least 70° C. Preferably,the semiconductor material is dried at temperature which does not exceed150° C., 140° C. or preferably 120° C.

A further embodiment of the inventive method concerns the application ofelectrodes. In this embodiment, at least two electrodes are applied toend faces of the semiconductor regions by depositing an electrodematerial onto at least one of the end faces or by providing theelectrode material, onto which at least one of the semiconductormaterials is applied. The electrode material used therefore ispreferably Au, Ag, Pt, Pd, an alloy or a compound of at least two ofthese metals, or any other conductive material used for the electrodes.The electrode material can be a metal, an alloy of at least two metals,at least one conductive polymer or an at least electrically conductingmetal compound. In particular, indium tin oxide (ITO) or otherelectrically conductive metal compounds can be used. Further, conductivepolymers can be used as electrode material, such as PEDOT:PSS orpolyaniline. The electrode material can be applied by vapor depositionor can be laminated onto the end faces of the semiconductor regions.Further, the electrode material can be attached to the at least one ofthe end faces using a conductive adhesive.

In addition, the electrodes can be provided with a contact region facingaway from the semiconductor material or can be provided with a conductorattached thereto, which is adapted for providing external contact.

Preferably, the ratio between the inner width of the openings and thethickness of the semiconductor region in which the openings are providedis at least 2, 4, 5, 10 or 20.

The present invention is illustrated by the following examples. Roomtemperature denotes a temperature from the range 18-23° C., the term“work function” denotes the vacuum work function, and percentages aregiven by weight (often abbr. wt.-%, or % b.w.), unless otherwiseindicated.

EXAMPLES Example 1

A glass substrate has been provided, onto which a gold electrode with athickness of 40 nm has been evaporated. Next, a DPP polymer according toExample 1 of WO2010/049321 (HOMO as determined by cyclicvoltammetry/Autolab PGSTAT® 30: |E_(H)|=5.35 eV) is applied in form of asolution of 5% of DPP in toluene. The solution containing 5% DPP isspin-cast at 1000 rpm and dried at 90° C. The spin-cast DPP forms afirst semiconductor region. In particular, the solution can be dried ata temperature of less than 50° C., or at room temperature (20° C.).

After having applied this first semiconductor region, a conductor regionis applied onto the semiconductor region in form of evaporated aluminiumwith a thickness of 40 nm (work function |E_(C)|=4.3 eV). The evaporatedaluminium is provided with openings by nanoimprint lithography. Theopenings have a diameter of 300-500 nm. The openings are arranged in agrid, wherein the openings have a center to center distance of 2 μm. Theratio of the cross-section area of the openings to the area of theconductor region is 0.196%.The thickness of the first semiconductorregion is 1 μm. The conductor layer has been applied by an evaporationtechnique, in particular by sputtering.

The openings are provided by a nano imprint stamp comprising a siliconwafer. The silicon wafer has a diameter of 100 mm. The stamp comprisesprojections with a height of ca. 135 nm and a diameter of 350 nm. Theprojections have a approximately circular cross section. The stamp hasbeen pressed onto the conductor region with a force of 20-80 N, inparticular with a force of 20-40 N. This force has been applied to thearea of the 100 mm silicon wafer. The resulting depressions within theconductor layer (and the underlying semiconductor layer) have a depth ofca. 100 nm and a width of 300-500 nm. The stamp is pressed into theconductor region at room temperature (20° C.). Preferably, the stamp ispressed into the conductor region at temperatures below 100° C., and inparticular below 50° C.

The stamp has been formed by UV lithography, wherein a resist is removedby oxygen plasma. The resulting structure is formed by isotrope dryetching.

After having applied the conductor region in form of a layer of 40 nmaluminium, a solution of 4% of DPP in dichlorobenzene is applied byinkjet-printing. The solution is deposited and dried at 75° C. Theresulting semiconductor region had an average thickness of 1 μm.

After having applied the second semiconductor region, an electrode ofgold with a thickness of 40 nm was applied by evaporation.

A current of 100 μA was achieved at a gate voltage of 3 V. Further, themobility was 0.05 cm²/Vs. The bulk charge carrier concentration was2×10¹⁵ cm⁻³ and the bulk conductivity was 500 Ωm. The thickness of thefirst semiconductor region was measured using a capacitance method. Themobility was measured with the resulting semiconductor structure in aFET configuration and the bulk charge carrier concentration was measuredwith a capacity/voltage method in the Schottky contact formed by theconductor region and the first semiconductor region. The transistor hada cross-sectional area of 0.1 mm² and the total number of openingswithin the conductor region was 24000.

With a semiconductor structure comprising DPP as semiconductor materialand aluminium as conductor material, Schottky contacts could be formedwith a bulk charge carrier density of 1-2×10¹⁵ cm⁻³ and a forward biasvoltage drop of 0.8-0.4 V. Further, a depletion width of 0.3-0.8 μmcould be yielded. These results refer to a semiconductor structure witha semiconductor region provided by spin-casting a solution of 4 or 5% ofDPP and a conductor region of 33 or 40 nm aluminium. The conductorregion was formed of aluminium with openings of 200-500 nm in diameter.

Example 2

In a second example, the conductor region was formed of an evaporatedaluminium layer of 40 nm with an inner width of the opening of 200 nm.The openings were arranged in grid with a center to center distance of500 nm. The semiconductor regions have been produced according toExample 1. In contrast to example 1, the openings in example 2 resultedresulted in a ratio of cross-sectional area of the openings to the areaof the conductor region of 0.126. As with Example 1, Example 2 yielded abulk current density at 3 V of 0.53 A/cm². The total number of openingsin Example 2 was 600000 for an area of 0.16 mm². As with Example 1, acurrent of 100 μA at 3 V has been yielded at a thickness of thesemiconductor regions of 1 μm measured with a capacitance method. Asregards bulk charge carrier concentration, conductivity and mobility,the same results as in Example 1 have been yielded.

In further examples of the invention using DPP as semiconductor materialand aluminium as conductor material, charge carrier concentrations of1.3×10¹⁵ cm⁻³ as well as a depletion width of 760 nm have been yielded.Further, charge carrier concentrations of 2.3×10¹⁵ cm⁻³ and a depletionwidth of 450 nm could be yielded with DPP as semiconductor material andaluminium as conductor material.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows an inventive semiconductor structure in form of a schematicdrawing.

DETAILED DESCRIPTION OF THE FIGURE

In FIG. 1, an embodiment of the inventive semiconductor structure isshown in a sectional side view. The depiction is not drawn to scale, inparticular with respect to the widths of the structure elements. Thesemiconductor structure comprises an electrode 10 with an electricalconnection 12. Electrode 10 is made of conducting material. Further, thestructure comprises a conductor region 20, which is provided withopenings 22. The openings 22 extend perpendicular to the direction alongwhich the conductor region 20 extends. Between the first electrode 10and the conductor region 20, a first semiconductor region 30 isprovided, which extends from the first electrode 10 to the conductorregion 20. On the side of the conductor region 20, opposed to thesemiconductor region 30, a second semiconductor region 40 is located.Further, a second electrode 50 is provided, together with an electricalconnection 52. The second electrode 50 is arranged on the side of thesecond semiconductor region 40, which is opposed to the conductor region20 as well as to the first semiconductor region 30. Therefore, the firstelectrode 10 as well as the second electrode 50 are located at opposedend faces of the semiconductor structure. In particular, the electrodes10 and 50 are located at end faces of the semiconductor regions 30 and40, which are opposed to the conductor region 20.

The structure shown in FIG. 1 is a layered structure such that theelectrodes 10 and 50, the conductor region 20 as well as the first andthe second semiconductor regions 30 and 40 are provided as layers with aconstant thickness. The openings 22 are filled with semiconductormaterial such that the first semiconductor region 30 and the secondsemiconductor region 40 are physically connected with each other by thesemiconductor material within the openings 22. The conductor region 20can be provided with an electrical connector in order to impose acertain voltage onto the conductor region 20.

For example, if a certain voltage is applied between the secondelectrode 50 and the conductor region 20, the semiconductor region 40in-between, i.e. the second semiconductor region, is modified as regardsits electrical properties. In particular, the voltage between theconductor region 20 and the second electrode 50 imposes an electricalfield within the second semiconductor region 40 which increases the bulkconcentration of free charge carriers or their equivalents within thesecond semiconductor region 40. Thus, if an additional voltage isapplied at the electrodes 50 and 10, a current is generated based on thefree charge carriers within the semiconductor regions 30, 40, the bulkconcentration of which is controlled via the voltage applied at theconductor region 20. In this way, a gain can be produced and the voltageat the conductor region 20 controls a current between the electricalconnections 12 and 52 of the first and second electrode 10, 50. Inparticular, by applying voltage difference between the electrodes 10 and50, the charge carrier movement is controlled by applying a voltage tothe conductor region 20. This voltage varies a depletion range locatedat the conductor region 20 and the semiconductor region 30. In addition,a depletion range located at the conductor region 20 and thesemiconductor region 40 can be varied. In this way, a channel for chargecarriers is opened, which travel from the semiconductor region 30 to thesemiconductor region 40 through the openings 22. If not voltage isapplied to conductor region 20, the depletion range covers the area of22, and charges do not travel through openings resulting in a transportcurrent between the semiconductor regions 30 and 40 of zero.

According to an exemplifying embodiment, the electrodes 10 and 50 can beformed of a layer of evaporated gold and the first and the secondsemiconductor region 30, 40 can be provided by layers of DPP, which arepreferably produced by casting the organic semiconductor materialdissolved in a solvent. Of course, after dissolved organic semiconductormaterial is applied, the solvent has to be removed before anotherstructural element is applied to the respective semiconductor region 30,40. The conductor region 20 can be formed of a layer of aluminium,preferably with a thickness of less than 100 nm or less than 50 nm. Theopenings 22 in the conductor region 20 are provided by nanoimprintinglithography into a layer of aluminium, which provides the conductorregion 20 and which is formed by evaporation of aluminium onto one ofthe semiconductor regions 30 or 40. The openings 22 have an inner widthof e.g. 500 nm.

REFERENCE SIGNS

10 first electrode

12 electrical connection

20 conductor region

22 openings

30 first semiconductor region

40 second semiconductor region

50 second electrode

52 electrical connection

CITED DOCUMENTS

-   -   WO 2010/049321    -   WO 2008/000664    -   US 2006/0086933 A1    -   US 2009/0001362 A1    -   Yu-Chiang Chao et. al., “High-performance solution-processed        polymer space-charge-limited transistor”, Organic Electronics 9        (2008), pp. 310-316    -   Yasuyuki Watanabe et. al., “Characteristics of organic inverters        using vertical- and lateral-type organic transistors”, Thin        Solid Films 516 (2008), pp. 2731-2734    -   US 2005/0196895 A1    -   US 2009/0042142 A1    -   U.S. Pat. No. 6,451,459 B1    -   WO 05/049695    -   WO 2010/049323    -   PCT/EP2010/053655    -   PCT/EP2010/054152    -   PCT/EP2010/056778    -   PCT/E P2010/056776

1. A semiconductor structure, comprising: at least one conductorregions; and at least two semiconductor regions, which are partlyseparated by the at least one conductor region, wherein: the at leastone conductor region comprises openings extending between semiconductorregions which are partly separated by a respective conductor region; atleast one semiconductor region comprises a diketopyrrolopyrrole polymeras a semiconductor material; the semiconductor regions comprise at leastone organic semiconductor material having a highest occupied molecularorbital energy level E_(H), E_(H) being defined by:5.0 eV≦|E _(H)|≦5.8 eV; and the conductor region comprises a conductivematerial having a work function E_(C) by:|E _(H)|−1.5 eV≦|E _(C) |≦|E _(H)|−0.4 eV.
 2. The semiconductorstructure of claim 1, wherein the organic semiconductor material has abulk concentration of positive charge carrier equivalents N_(p) withN_(p)≦1×10¹⁶ cm⁻³, N_(p)≦8×10¹⁵ cm⁻³, N_(p)≦6×10¹⁵ cm⁻³, N_(p)≦5×10¹⁵cm⁻³, N_(p)≦10¹⁶ cm⁻³, N_(p)≦4×10¹⁵ cm⁻³, N_(p)≦2×10¹⁵ cm⁻³ , orN_(p)≦1×10¹⁵ cm⁻³.
 3. The semiconductor structure of claim 2, whereinE_(H), E_(C), and N_(p) are adapted to yield a depletion width I_(d) ofmore than 100 nm within the semiconductor region.
 4. The semiconductorstructure of claim 1, wherein the at least one organic semiconductormaterial comprises a diketopyrrolopyrrole (DPP) polymer having one ormore DPP skeletons represented by the following formula:

in the repeating unit, wherein: R¹ and R² are the same or different fromeach other and are selected from the group consisting of hydrogen; aC₁-C₁₀₀ alkyl group; —COOR³; a C₁-C₁₀₀ alkyl group which is substitutedby one or more halogen atoms, hydroxyl groups, nitro groups, —CN, orC₆-C₁₈ aryl groups and/or interrupted by —O—, —COO—, —OCO—, or —S—; aC₇-C₁₀₀ arylalkyl group; a carbamoyl group; a C₅-C₁₂ cycloalkyl groupwhich can be substituted one to three times with a C₁-C₈ alkyl groupand/or a C₁-C₈ alkoxy group; a C₆-C₂₄ aryl group, and pentafluorophenyl;and R³ represents a C₁-C₅₀ alkyl group.
 5. The semiconductor structureof claim 4, wherein the DPP polymer is selected from the groupconsisting of a polymer of formula (Ia):*A_(n)*   (Ia), a copolymer of formula (Ib):*A-D_(n)*   (Ib), a copolymer of formula (Ic):*A-D_(x)B-D_(y)_(n)*   (Ic), and and a copolymer of formula (Id):*A-D_(r)B-D_(s)A-E_(t)B-E_(u)_(n)*   (Id), wherein: x=0.995 to0.005; y=0.005 to 0.995, with the proviso that x+y=1; r=0.985 to 0.005;s=0.005 to 0.985; t=0.005 to 0.985; u=0.005 to 0.985, with the provisothat r+s+t+u=1; n=4 to 1000; A is a group of formula (X):

wherein a′=1, 2, or 3; a″=0, 1, 2, or 3; b=0, 1, 2, or 3; b′=0, 1, 2, or3; c=0, 1, 2, or 3; c′=0, 1, 2, or 3; d=0, 1, 2, or 3; d′=0, 1, 2, or 3;with the proviso that b′ is not 0 if a″ is 0; Ar¹, Ar^(1′), Ar²,Ar^(2′), Ar³, Ar^(3′), Ar⁴ and Ar^(4′) are independently of each otherheteroaromatic or aromatic rings, which optionally can be condensedand/or substituted; D is —CO—, —COO—, —S—, —O—, or —NR¹¹²—; E is C₁-C₈thioalkoxy, C₁-C₈ alkoxy, CN, —NR¹¹²R¹¹³, —CONR¹¹²R¹¹³, or halogen, R¹¹²and R¹¹³ are independently of each other H; C₆-C₁₈ aryl; C₆-C₁₈ arylwhich is substituted by C₁-C₁₈ alkyl, or C₁-C₁₈ alkoxy; C₁-C₁₈ alkyl; orC₁-C₁₈ alkyl which is interrupted by —O—; B, D and E are independentlyof each other a group of formula:*Ar⁴_(k) ^(Ar) ⁵_(l)Ar⁶_(r)Ar⁷_(z)*, or formula (X), with theproviso that in case B, D and E are a group of formula (X), they aredifferent from A, wherein k=1; l=0 or 1; r=0 or 1; z=0 or 1; Ar⁴, Ar⁵,Ar⁶ and Ar⁷ are independently of each other a group of formula:

wherein one of X⁵ and X⁶ is N and the other is CR¹⁴; and R¹⁴, R^(14′),R¹⁷ and R^(17′) are independently of each other H, or a C₁-C₂₅ alkylgroup, which may optionally be interrupted by one or more oxygen atoms.6. The semiconductor structure of claim 5, wherein the DPP polymer is apolymer according to formula (Ib-1), (Ib-9), (Ib-10):

wherein: R¹ and R² are independently from each other a C₈-C₃₆ alkylgroup; and n=4 to
 1000. 7. The semiconductor material of claim 1,wherein the organic semiconductor material has a polydispersity in therange of from 1.01 to
 10. 8. The semiconductor structure of claim 1,wherein the openings comprised in the conductor region have an innerwidth of more than 200 nm.
 9. The semiconductor structure of claim 1,wherein the conductive material of the conductor region comprises ametal, an alloy, or a conductive polymer.
 10. The semiconductorstructure of claim 1, further comprising at least two electrodes at endfaces of the semiconductor regions, wherein the electrodes as well asthe conductor region each comprise a contact region or are provided witha conductor adapted for external contact.
 11. The semiconductorstructure of claim 1, wherein: the semiconductor regions which arepartly separated by the respective conductor region are in directcontact with each other through the openings of said conductor region;and the semiconductor regions are separated by the respective conductorregion by sections of the respective conductor region, which sectionsare lateral to the openings.
 12. The semiconductor structure of claim 1,comprising a conductor region partly separating two semiconductorregions, wherein: the conductor region and the two semiconductor regionsprovide a vertical transistor structure; and the conductor regionprovides a gate adapted for conductivity control between thesemiconductor regions.
 13. A semiconductor structure, comprising: atleast one conductor region:, and at least two semiconductor regions,which are partly separated by the at least one conductor region,wherein: the at least one conductor region comprises openings extendingbetween the semiconductor regions which are partly separated by therespective conductor region; the semiconductor regions comprise at leastone organic semiconductor material which is at least one DPP polymer;and the conductor region comprises a metal selected from the groupconsisting of Al, Cr, Cu, Fe, In, Sb, Si, Sn, and Zn.
 14. A method forproducing the semiconductor structure of claim 1, the method comprisingpartly contacting the at least two semiconductor regions through theopenings of the at least one conductor region.
 15. The method of claim14, further comprising embossing, mechanically cutting, or laser cuttingthe openings with an inner width of more than 200 nm through acontinuous layer, wherein the at least one conductor region is thecontinuous layer of the conductive material.